Time Transgressive Submarine Slope Confinement, Increased Flow Efficiency and the Growth of Basin-Floor Fans

Abstract

Observations from outcrop, modern and subsurface datasets indicate that key regressive surfaces formed during phases of submarine slope degradation are time transgressive. These include levee deposits overlying lobes, composite erosion surfaces recording multiple phases of cut and fill, and hanging valleys and cut-off sinuous bends. Progressive confinement on the slope results in sequential sediment gravity flows maintaining their downslope energy farther into the basin during the initial period of slope channel system evolution. In this way, frontal lobes are continuously incised and overlain by external levees as the channel system propagates farther into the basin and becomes more confined at a reference point on the slope by a combination of substrate erosion and levee construction. The stratigraphic response of the linked basin floor fan is growth and net progradation until a maximum basinward extent is reached, corresponding to the time of most efficient slope sediment supply, which marks a maximum regressive surface. Conceptually, this process response could be autocyclic, but would be amplified with an allogenically-driven waxing-then-waning sediment supply cycle. The coupled progressive confinement of the slope channel system and basinward growth of submarine fans will result in a strongly diachronous lithological basal surface to the system and the widespread downstream transition from levee deposits to lobe deposits. This challenges the widely applied lowstand model whereby the deep-water sequence boundary is isochronous and passes into a correlative conformity at the base of the basin floor fan.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015